The present invention relates to a magnetic core of motors, transformers, etc., which are used as peripheral apparatuses for a hard disc, a polygon mirror and the like.
As these apparatuses, used for office automation (referred to as OA hereinafter) apparatuses, have been miniaturized, and a high performance has been achieved more and more, recently, volume reduction and miniaturization of a magnetic core of motors have been sought. A high-insulating coated film which is thin and has no pinhole is required for the surface of a thin magnetic core so as to increase an effective area of winding. In order to obtain excellent output characteristics, an electrodeposition coating has recently exclusively been used in place of a powder coating which has hitherto been used. However, regarding almost all of electrodeposition coating compositions which are put to practical use, polyisocyanates have heretofore exclusively been used as a crosslinking agent. In addition, as a curing agent for efficiently carrying out the crosslinking reaction, organic tin compounds have been used.
On the other hand, as the precision of OA apparatuses is improved, a phenomenon in which clouding, of unknown origin, is formed on the surface of a hard disc (magnetic disc) or a polygon mirror, used for these apparatuses so as to cause a wrong operation or printing failures has become a problem. In the process of examining the cause, it has become apparent that the problem is caused by the fact that organic tin compounds contained in the coating composition to be used for a motor or a transformer, which drives the hard disc or are polygon mirror or provided at the periphery thereof, is activated by chlorine, water, etc. and gasified to be adsorbed on the surface of the hard disc. It has been found that, in case of a motor for driving a hard disc and a motor for a polygon mirror driving an apparatus, the apparatus is in the closed state so that the hard disc or polygon mirror becomes cloudy even if a gas containing a trace amount of tin is vaporized.